Web Quick Conversion Chart Of Mm To Inches. The millimeter (si symbol mm) is a unit of length in the metric system, equal. 10 mm to inches = 0.3937 inches. 30 mm to inches = 1.1811. 1Mm = (1/25.4)″ = 0.03937007874″ The Distance D In Inches (″) Is Equal To The Distance D In Millimeters (Mm) Divided By 25.4: 1 mm to inches = 0.03937 inches. 30 mm to inches = 1.